The present invention relates to a magnetron plasma apparatus and, more particularly, to a magnetron plasma apparatus used for sputtering or etching of a semiconductor substrate.
FIG. 1 shows an example of a conventional magnetron sputtering apparatus. In FIG. 1, disk-like target 2 is placed on concentric electromagnet 1, and lines 3 of magnetic force of electromagnet 1 leak onto the surface of target 2. As shown in FIG. 2, a parallel magnetic field on the surface of target 2 is radial with respect to a central axis of electromagnet 1. Target 2 is connected to plasma power source 4 so as to be a cathode. A plasma is generated above target 2 by source 4.
In the apparatus having the above arrangement, dissociated electrons in the plasma perform doughnut-like cyclotron movement which is caused by the electric field near target 2 and the parallel magnetic field near the surface of target 2. The dissociated electrons are looped in a ring of the doughnut-like cyclotron movement due to the cyclotron movement of the dissociated electrons, thereby increasing a plasma density.
This phenomenon will be described in more detail with reference to FIGS. 3 and 4. As shown in FIG. 3, an ion sheath portion is formed between the plasma and the target. No plasma is present in this ion sheath portion. Without the parallel magnetic field, distribution of the plasma density along distance from the target surface is substantially uniform above the ion sheath portion, as shown in FIG. 3. However, with the parallel magnetic field, the dissociated electrons perform cyclotron movement due to the parallel magnetic field and the electric field. As a result, as shown in FIG. 4, the plasma density is increased. More specifically, when the intensity of the magnetic field is smaller than a critical intensity (normally about 100 gauss), the plasma density is rarely increased. However, when the intensity of the magnetic field is larger than the critical intensity, both the plasma density is increased with a magnetic field intensity. In this case, since the parallel magnetic field is monotonously decreased against the distance from the target surface, the plasma density is maximized near an interface where plasma contacts the ion sheath. On the other hand, the parallel magnetic field intensity on the target surface is maximized at a central portion (denoted by A) between both magnetic poles of the electromagnet, as shown in FIG. 5. That is, a maximum region of the plasma density is an extremely localized region, i.e., a region near the surface which contacts the ion sheath portion at portion A.
In the above sputtering apparatus, a voltage of 500 to 800 V is normally applied to the ion sheath portion, so that ions are extracted from the plasma by the electric field, accelerated, and then emitted onto the target, thereby causing sputtering.
According to the above sputtering apparatus, however, maximum region 5 of the plasma density caused by the cyclotron movement of the dissociated electrons is localized near the ion sheath surface, as shown in FIG. 6. Therefore, ions are extracted from this localized region by the voltage applied to the ion sheath portion. For this reason, sputtering or erosion occurs at only localized region 6 of the target. As a result, the effectiveness of the target is degraded, uniformity of a film thickness is degraded when a film is deposited on a substrate placed opposite to the target, and nonuniformity of step coverage appears.